10 
ANATOMICAL STRUCTURE OF TREMATODES. 
The following technical description shows the systematic position 
and general structure of the flukes under discussion: 
[Suborder Malacocotylea: Digenea. Families Monostomidae, Fasciolidae, Param- 
phistomidae, and Schistosomida?. See figs. 13-15, 18, 20, 42-47, 49-50, 64, 
67—68, 78, 85-86.] 
IVith the exception of the blood flukes {Schistosoma) they are all hermaphrodites. 
They are flat, cylindrical, or conical worms, always longer than broad; on the ante- 
rior extremitw is situated the mouth, surrounded by a muscular organ, known as the 
oral sucher and curved slightly ventrad. There is a second sucker (the acetabulum), 
which is situated in the ventro-median line; in the Fasciolidae the acetabulum is gen- 
erally fomid on the anterior half of the body, while in the family Paramphistomidfe 
it is at or near the posterior extremity. The surface of the worms is generally more 
or less covered with minute spines or tubercles. 
The digestive tract consists of the mouth, a short esophagus, and two blind sacs 
(intestinal ceca), which represent the true intestine. The anterior portion of the 
esophagus is generally connected with the mouth by a muscular bulb (the pharynx)', 
the posterior extremity bifurcates, one branch being connected with each intestinal 
cecum. The intestinal sacs are usually simple elongated tubes (fig. 43), but in the 
genus Fasciola they branch freely (fig. 20, i). In Schistosoma the two ceca unite 
after passing the genital glands. An anus is never present. 
Genital organs. — The genited pore is in the ventro-median line in nearly all species 
here described, the male copulatory organ {cirrus, or penis,) lying very close to the 
female opening {vulva). Male organs: A cirrus is frequently seen extruded from the 
genital pore, and in these cases it appears as a curved organ, varying in size accord- 
ing to the ^pscies; usually the cirrus is invaginated into the cirrus pouch. Through 
its center runs a canal (the ductus ejaculatoris), which receives the spermatozoa from 
a vesicula seminalis. The latter is partially or entirely included in the pouch; at its 
posterior end it receives either directly or indirectly the two va.sa etferentia, through 
which the spermatozoa are conducted from the testicles. The testicles, generally two 
in number, one right and one left, are more or less round, lobate, or branched. Female 
orgam: The vulva leads into a canal, the anterior portion of which is known as the 
metraterm; this is continued as the iderus, which forms more or less numerous folds in 
the median portion of the body, and finally leads to the so-called shell-gland, which 
may frequently be seen in fresh specimens {Fasciola rnagna and others) as a round 
body a short distance posterior of the acetabulum. In the center of the shell-gland is 
a canal (the ootype), in which four canals {uterus, oviduct, Laurer's canal, and vitelloduct) 
come together. The ovary in some species is globular, in others lobate, or branched, 
and connects with the ootype through the oviduct. The Laureds canal runs from 
the ootype dorsad, and opens to the exterior on the dorsal surface. Its function is 
still doubtful, but homologically it represents the uterus of cestodes. The vitellogene 
glands (vitellaria) are two in number, and are situated laterally of the longitudinal 
intestinal ceca; they vary in size in different species, are generally quite elongated, 
and are composed of numerous branches, or acini, much like a bunch of grapes in 
form, all of which connect with a longitudinal vitelloduct (one on each side of the 
body); these longitudinal ducts are in turn connected by a pair of transverse ducts 
which unite in the median line, immediately posterior of the shell-gland, to form a 
common reservoir; this, in turn, empties into the ootype through the short vitello- 
duct mentioned above. The vitellaria produce yolk cells, which are associated with 
the true ovum to form the eggs. 
Excretory system. — At or near the posterior extremity, generally somewhat dor- 
sally, is situated a small pore {porus e.rcretorius), which leads into a median terminal 
